Method for generating and transmitting sonic vibrations



Jan. 3, 1967 D JR -3,295,837 I METHOD FOR GENERATING AND TRANSMITTING SONIC VIBRATIONS Original Filed July 6, 1959 2 Sheets-Sheet 1 INVENTOR. In ZG Z 3055122 JP Jan. 3, 1967 Original Filed July 6, 1959 A. e. BODINE, JR 3,295,837

METHOD FOR GENERATING AND TRANSMITTING SONIC VIBHATIONS 2 Sheets-Sheet 2 INVENTOR.

United States Patent 3,295,837 METHOD FOR GENERATING AND TRANS- MITTING SONIC VIBRATIONS Albert G. Bodine, Jr., Los Angeles, Calif. (7877 Woodley Ave., Van Nuys, Calif. 91406) Application Sept. 12, 1960, Ser. No. 55,537, now Patent No. 3,153,530, dated Oct. 20, 1964, which is a division of application Ser. No. 825,117, July 6, 1959, now

Patent No. 2,960,314. Divided and this application Oct. 8, 1964, Ser. No. 402,529

4 Claims. (Cl. 2591) This application is a division of my application entitled Apparatus for Generating and Transmitting Sonic Vibrations, Serial No. 55,537, filed September 12, 1960 now Patent No. 3,153,530, which was a division of my application entitled Method and Apparatus for Generating and Transmitting Sonic Vibration-s, Serial No. 825,117, filed July 6, 1959, now Patent No. 2,960,314. Said application Serial No. 825,117 was a continuation-in-part of my prior and parent application, Serial No. 484,627, filed January 28, 1955 and entitled Apparatus for Generating and Transmitting Sonic Vibrations, now abandoned.

This invention relates generally to method-s for the generation and transmission of relatively high power by means of intense sonic vibrations, particularly for the generation or transmission of sonic vibrations in resonant vibratory mechanical devices, either elastically deformable vibratory bodies of the distributed constant class, or elastically supported bodily vibratory devices of lumped constant characteristics.

A large number of industrial uses for high power sonic vibrations have been discovered. It is known, for example, that intense sonic energy may be applied to gases, liquids or solids to produce certain desired chemical or physical effects. Many types of power tools or other equipment are operated by sonic energy of high intensity. One illustrative example involves a longitudinally extended elastic bar, in which a longitudinal resonant standing wave is set up and maintained, so that an end portion of the bar becomes the location of a velocity antinode of such standing wave, and is utilized to vibrate a bit or other tool against the work. Other modes of vibration, such as lateral or gyratory (see my Patent No. 2,960,314) are within the scope of the invention.

The bodies or devices to be sonically vibrated at resonance are often characterized by high acoustic impedance. They vibrate with great force, and with small velocity amplitude. The problem of driving these devices, i.e., the provision of an effective vibration generator suited thereto, is often very difiicult, particularly in view of the fact that ordinary practically available sources of motivating power operate at low impedance, characterized by driver elements moving with relatively low force but substantial velocity. Ordinary low impedance drivers are incapable of driving high impedance devices because of the mismatch of impedance. The efliciency of transduction has been characteristically low.

The common sonic generators, such as magneto-striction bars, crystals, etc., are capable of a motion of only a few feet per second by reason of limitations set by elastic strain limits, which motion I have found to be entirely inadequate for high power applications.

Mechanical generators are known which have the requisite motional characteristics but suffer from complexity and a host of ensuing problems. Any degree of complexity of moving parts results in various vibratory interactions taking place at high frequency between these parts, with consequent high energy loss and frequent destruction of parts in high stress applications. At very high frequencies gears will chatter, bearing separators seize and fracture, and the individual balls or rollers of anti friction bearings are forced to rotate so fast they become unstable in their motion. Plain journal bearings seize and overheat. The power of previously known generators has been relatively low, particularly at the higher frequencies; and the ruggedness required of an industrial machine has been lacking. Many proposed industrial applications of sonic power have been correspondingly handicapped.

It is accordingly the primary object of the present invention to provide a novel and improved sonic vibration generating method and apparatus particularly suited to various industrial applications and characterized by relatively high power output, efficiency of transduction, simplicity and ruggedness.

The invention is practiced in systems involving the driving of an inertia mass rotor in an orbital path under guiding constraint of a bearing means, whereby a periodic force impulse is exerted on the latter, and the coupling of this bearing means to a vibratory device having a resonant frequency range whereby said periodic force impulse, or a component there-of, is effective to vibrate said device in said range. To this end, the rotor is driven at an orbital frequency which generates a vibration frequency in the range of resonance for the driven vibratory device. I have discovered that the driven vibratory device, when so vibrating in its resonance range, with its vibration amplitude amplified by resonance, back-reacts with or has a feedback to the orbital rotor, strongly constraining the rotor to an orbital periodicity corresponding to its own resonant frequency. I have further discovered that the apparatus tends inherently to operate on the low side of the frequency for peak resonant amplitude, and further, that the whole apparatus, driven vibratory device and orbiting rotor, tends to lock in synchronously slightly below the frequency for peak resonant amplitude. The orbiting rotor is strongly constrained to produce this frequency, and although it could of course be strongly enough driven to reach a threshold condition where it would reach and break over peak amplitude resonance frequency, considerable increase in driving effort is required before this unwanted condition occurs. In this connection, it is to be understood that in the practice of the invention the driving effort on the rotor is limited to a value below such threshold condition. The rotor is hence guarded from overspeeding and destroying itself or its housing when operated at high frequency.

In addition to these elfects, the constraint which keeps the frequency of the orbiting rotor to the low side of hte resonance curve (amplitude vs. frequency) of the vibratory driven device is effective to establish a phase angle between the rotor motion and the motion of the vibrating device wherein maximum power is delivered from the rotor to the vibrating device fora given power input to the rotor.

It will be evident that such an orbiting rotor generator has high output impedance, while being operable by motive power at low impedance, impedance being understood to be proportional to the ratio of force to velocity. Considering the output side of the generator, where the race for the orbiting rotor is coupled to the vibratory driven device, it will be seen that the cyclic force amplitude will be high owing to the high magnitude of centrifugal force, while the stroke amplitude, and therefore the velocity amplitude, Will obviously be low. The desirable high output impedance for the resonant system is therefore attained. Impedance is generally thought of in connection with alternating phenomena such as alternating forces, in comparison with resulting velocity amplitude. The motive power source used in the present instance is typically a continuous air jet, rather than an alternating entity. Nevertheless, the continuous air jet has the characteristic of relatively low force and relatively high velocity, and is, broadly speaking, a form of'power having a low impedance quality. The generator of the invention thus fulfills the requirement of operating oif a low impedance form of power, and delivering power at high impedance.

The illustrative embodiments chosen for disclosure herein are of the type wherein the resonantly driven device is of the distributed constant type, though without implied limitation thereto. It should be explained that a distributed constant system is one wherein the parameters of mass and elasticity governing the resonant vibration frequency are distributed throughout all or a significant part of the vibratory system, as in the ideal example of a tuning fork. By contrast, a lumped constant system is one wherein the parameters of mass and elasticity governing the resonant frequency are largely concentrated or localized in discrete elements such as intercoupled masses and springs, respectively. Of course, these are idealized classifications. Practical systems usually are mixtures of the two. Thus, practical systems wherein the parameters of mass and elasticity are preponderantly distributed will also very commonly have local concentrations of mass, with small capability for elastic vibration therein; While practical systems wherein mass and elasticity are preponderantly localized, as in intercoupled spring and mass elements, will invariably have certain distributed constant qualities in view of mass inherently present in spring elements, and elasticity inherently present in mass elements. Thus, the resonantly driven devices of the invention may embody such distributed constant elements as an elastic bar, in which either transverse, gyratory, or longitudinal standing Wave action may be set up by the vibration generator. Such bar may be a solid rod, or it may be tubular, as a steel pipe. The term bar is often used in the field of acoustics in connection with discussions of elastic Wave propagation, without reference to the cross sectional form of the bar, and the term will be so used herein, both in the specification and claims, thus generically comprehending hollow rods, or pipes, as well as solid rods, I- 'beams, and other structural shapes.

The orbital inertia-mass rotor of the foregoing discussion may take any of several advantageous forms within the scope of the present invention, among which are a spherical or cylindrical rotor rolling around the inside of a circular, or elliptical, raceway or bearing surface, driven, for example by means of an impinging fluid stream, or, as another desirable example, a ring whirling on a bearing means in the form of a pin, also driven by a stream of air. Such devices are disclosed in various forms in my aforesaid Patent No. 2,960,314, which is incorporated herein by this reference.

The invention to which the present application is directed involves my discovery that a plurality of such freerolling or whirling orbital rotors such as described immediately above, when acoustically coupled to a single sonically vibratory driven member, can be made to lock-in to the resonant frequency range of the resonant member more perfectly than can a single such rotor. That is to say, better frequency control is available in a resonant system when the rotor means is subdivided into a plurality of individual rollers rather than being concentrated in a single more massive roller.

As mentioned hereinabove, a free running rotor couples in to a resonantly vibratory member by virtue of the relationship of its cyclic impulse force applied to the resonant member, and the cyclic back reaction or feedback force exerted by the resonant member on the rotor. A high Q resonant member has a strong back reaction or feedback, and commonly tends to dominate the rotor means and to control the latter fairly well to its resonant frequency range. On the other hand, a rotor with a relatively large orbiting mass, strongly driven and well acoustically coupled to the resonant member, has in some cases an ability or a tendency to override the resonant member and, in a dominant manner, to force drive the resonant member at a forced frequency, somewhat off the desired resonant frequency range. This may occur especially if the speed of the rotor is changed quickly, or is brought up to operating speed rather suddenly.

The discovery of the invention is that by the use of a plurality of smaller rotors, in place of one roller of large orbiting mass, a large total, effective or resultant force impulse can be attained, while still maintaining good dominance of the resonant member over the individual rotors as regards frequency stability. The unique and unexpected performance involved here can best be described by running through a description of a typical starting operation of a plural rotor system. Assume, for example, an air driven plural rotor system. The rotors may either be balls or cylinders rolling inside a circular bearing means, or an inertia ring whirling on a bearing pin, and in either case, it may be assumed that the rotors are driven by air jets from suitable fluid nozzles. In such a system, there will inevitably be slight manufacturing difference resulting in differences in rolling friction, fluid nozzles, air temperature, etc., so that when the air source is first turned on and the several rotors come up in speed, there is inevitably at least a slight difference in their speed at any given instant of time. There is, of course also a minor tendency for the rotors to run in a sort of synchronism, sometimes mistakenly called resonance," because of the bodily vibration of the rotor housing. This is a previously known low order effect, usually with undesirable phase relationships, and having no relation to the controlling factors operating in the present invention involving cooperation with a elastic resonance phenomena. For example, such a effect involving bodily vibration synchronism is described in High No. 2,496,291, which is a non-acoustic case, and therefore does not involve the unique controlling effect of the system of the present invention, Le, a sonically derived back reaction on the rotor which automatically increases in magnitude as peak resonance frequency is approached. To return from this digression, the important point here is that the rotors, as they come up in speed, do not all reach the resonant frequency range simultaneously.

As soon as the fastest rotor reaches the resonant frequency range of the resonant vibratory member, the latter vibrates in stable fashion at this frequency, exerting the aforementioned back reaction on this first rotor, and thus holding the speed of the first rotor at thi resonant frequency as a back-coupled acoustic system. It will be seen that there is, in effect, a feedback of frequency control from the resonantly vibrating device driven by the rotor, to'the rotor which is doing the driving. The ensuing few cycles with this first rotor at resonant frequency then build up a substantial vibration amplitude in the resonantly vibratory member.

Now, having the resonant member vibrating at said relatively strong amplitude, there is a strong monitoring back reaction or feedback effect to hold the next rotor coming up to speed at or within the desired resonant range. This then builds up the resonant amplitude still further, so that the system is even more strongly stabilized for the next rotor, and so on.

The result is that the total impulse of all the rotors can thus be high, using small rotors, but a number of them, thus attaining a system of high impulse which still is not force driven at whatever frequency some one largemass dominant rotor might happen or choose to run. The resonant vibratory member thus has a much improved dominating influence as regards resonant frequency stability. If any one of the rotors should have a tendency to peed up, after the system has become stabilized, its phase angle and power factor relative to the resonant member becomes such that this rotor then is forced to pick up more than its share of the load, which is of course an immediately retarding influence on the rotor. Thus a reasonably equalized driving force driving the several individual rotors has the effect of strongly tending to prevent any one rotor taking very much more than its share of the 5. load, and hence this powerful, multi-rotor system in this acoustic combination has very great frequency stability.

Some examples of systems embodying the invention will now be considered, reference for this purpose being had to the accompanying drawings, in which:

FIG. 1 is an elevation, partly in longitudinal section, showing one embodiment of the invention;

FIG. 2 is a longitudinal section taken in accordance with the broken line 22 of FIG. 1;

FIG. 3 is a small scale diagrammatic view of another embodiment of the invention;

FIG. 4 is a view partly in elevation and partly in longitudinal section of the embodiment of FIG. 3, a portion of the elastic bar of FIG. 3 being broken away;

FIG. 5 is a section taken on line 55 of FIG. 4; and

FIG. 6 is a section taken on line 66 of FIG. 4.

In FIGS. 1 and 2, I have shown an embodiment of the invention applied to a sonic-abrasive polishing or grinding machine, and characterized illustratively as the case wherein the sonic generator is arranged to set up longitudinal vibrations in an elastic bar, as distinguished from the transverse or gyratory vibrations. In FIG. 1, numeral 10 designates generally a cylindrical elastic bar, composed of some good elastic material such as steel, to the lower end of which has been secured a polishing or grinding head 11 having a flat and extremity 12 adapted to be applied to the surface of the work 13, the work being clamped, as indicated at 14, to the moving bed of a milling type machine fragmentarily indicated by the reference numeral 16.

The bar 10 is resiliently clamped near its upper end by a compliant rubber block or sleeve 17 carried by a suitable supporting ring 18 on an arm extending laterally from a suitable means of support indicated generally at 19.

The sonic vibration generator, designated by numeral 20, comprises a cylindrical body 21 formed at its lower end with a threaded coupling pin 22 screwed into an internally threaded box 23 at the upper end of rod 10. The upper reduced end portion 24 of the body 21 has a fluid passage 25 extending therethrough, to which is coupled, as indicated at 26, a hose 27 understood to be supplied with air under suitable pressure. The body 20 includes a removable body part 20a, meeting the remainder of the body on a vertical medial parting plane 28, and secured in position by suitable screws as shown in FIG. 2. A vertical series of circular chambers 29, here two in number, are formed in the body 20, between the main body part and the insert part 20a, as clearly shown, and axles 30 intersect these chambers, being mounted in the body as illustrated. These axles, whose central portions are preferably crowned, as indicate-d at 31, support inertia rings 32. The rings 32 are adapted to be rolled about the axles 30 and the centrifugal force of the spinning ring is exerted on the generator housing or body through the axles 30.

'The aforementioned fluid passage 25 joins the upper cavity 29 in a tangential direction, as shown; and a passageway 34 extends tangentially to the upper cavity 29 and also tangentially to the lower cavity 29, the arrangement being such however, that the fluid introduced to the two cavities will spin in opposite directions as compared with one another. A tangential outlet passage 35 leads outwardly through the side of the generator body, and the discharged -fluid may be received by a stationarily positioned outlet pipe 36, supported separately of the generator.

The inertia rings 32 in the upper and lower cavities are caused to roll on their axles 30, in opposite directions of rotation by the stream of pressurized air introduced tangentially thereto, as earlier described. As will appear, the air from the source is introduced tangentially to the upper chamber 29, spinning thereabout and forcing the ring 32 to roll about the axle 30. Some of this air is constantly discharged tangentially via the passage 34, to be introduced to the lower chamber 29 in a tangential direction, spinning about the latter chamber in a direction contrary to the spin direction 'for the chamber immediately above, and accordingly causing the lower ring 32 to spin with a direction opposite to that of the upper ring 32. Air from lower chamber 29 is also constantly discharged tangentially via the outlet passage 35.

In general, pressure fluid circulated successively through the chambers 29 would cause the described rotations of the inertia rings, but without frequency control, and the phase relations between the two rings would be at random. However, when the rings are driven by the stream of pressure fluid so as to spin about the axles at a number of revolutions per second approaching or approximating the resonant frequency of the rod 10 for a longitudinal mode of elastic vibration, the rod 10, as a result of some initial force impact received from the generator, is started into its longitudinal mode of resonant standing wave vibration. The first characteristic longitudinal vibration which will occur is in general that of a free-free bar (i.e., one not rigidly clamped at its ends) vibrating at half wavelength. In this mode of longitudinal resonant vibration, the longitudinal center region of the bar tends to stand substantially stationary while the two opposite end portions thereof alternately move away from and then back toward one another. The bar thus alternately elastically elongates and contracts. It will be seen that as this resonant type of motion begins to be set up in the rod 10, the sonic generator 20 mounted on its upper end is vibrated longitudinally at the resonant frequency of the rod 10. As a result of this action, the spinning inertia rings 32 synchronize with the longitudinal motion of the upper end portion of the rod 10, and therefore with one another. In other words, the rings orient themselves, though spinning in opposite directions, so as to move in a power-delivering phase relationship in the direction longitudinally of the resonantly vibrating rod 10. Moreover, as the rings thus synchronize themselves with the resonantly vibrating rod, and thus with one another, the vertically directed forces which they exert through the generator body against the upper end portion of the rod synchronize with one another, so that the forces become fully additive in the direction longitudinally of the rod.

To consider the action involved in this process more closely, it will "be evident that one of the rings will inevitably speed up faster than the other, and will thus be the first to obtain resonant frequency. This results, as explained still more fully in the introductory .part of the specification, in resonant vibration of the rod or bar, at resonantly augmented amplitude, and results also in the previously described resonance-induced back reaction or feedback control whereby the ring is constrained against speeding over the resonant frequency range. The second ring then comes up to resonant speed, and is held thereto by the already stabilized vibration in the resonant frequency range. The two rings are thus each synchronized with the rod, and then with each other by the elastic resonant phenomena described. Both are thus under the dominating frequency control of the resonantly vibrating elastic bar. If additional rings were to be provided, the beneficial effect and advantage of the invention would merely be further extended, each ring coming under control in its turn in the resonant frequency range. Upon synchronism of the rings 32 being thus achieved at stabilized resonant frequency, maximum effective force is delivered to the vibratory rod 10 in the direction longitudinally thereof, maintaining the same in high amplitude longitudinal half-wave elastic vibration.

The resonant frequency standing wave set up in the rod 10 thus causes the fluid driven inertia rings 32 to lock in at resonant frequency, and as I have found, on the lower side of the resonant curve, with all rings dominated by the resonant vibration of the bar by the described resonant back reaction of feedback.

Considering further the operation of the tool as a whole, a hose 37 supplies liquid carrying fine particles of abrasive to a nozzle 38 which is directed to the area of the work engaged by the work head 11. According to principles understood in the art, the sonically vibrated work head 11, in cooperation with the abrasive particles carried by the fluid supplied from nozzle 38, generates cutting, grinding or polishing action on the Work piece 13. Depending upon the type of polishing or cut desired, various results can be obtained. As shown, the original surface of the workpiece is being cut or ground to form a finished surface 13a, this being achieved by passing the work-piece past the working head 11 at right angles. As known in the art, longitudinal holes can also be formed in the workpiece by the obvious step of advancing the cutting tool toward the work, or, of course, advancing the work toward the working head.

FIGS. 36 illustrate another application of the invention, the purpose being, in this instance, sonic vibration of the bottom wall of a liquid tank for purpose of sonic agitation of the contents thereof for any desired purpose.

A sonic vibration generator 40 is flange-connected at its upper end to the lower end of a solid elastic rod 41, the upper end of which is flange-connected to the bottom of liquid tank 41a.

The sonic generator 40 comprises a vertically elongated housing or body 41b, formed with a vertically arranged series of circular cavities or chambers 42, the latter opening through one side of the body 41b, as shown in FIG. 6, and being closed by a cover plate 43a. In each such cavity 42 is a steel ball 44, of substantially lesser diameter than the major diameter of the cavity 42, and adapted to be rolled around the inner peripheral rolling bearing surface 42a of the chamber as a raceway by tangentially injected fluid under pressure.

Connecting to fluid passage 46 in the lower end of body 40 is fluid supply hose 47. The passage 46 joins the lowermost chamber 42 tangentially, as shown in FIG. 4, and a fluid passage 43 extends tangentially from the upper side of chamber 42 to the lower side of the chamber 42 next above, it being noted that the tangential passages are so arranged that the direction of spin is reversed from each chamber to the chamber next above. The entire series of chambers 42 are similarly connected by tangential passageways 43, and from the uppermost chamber 42 there leads a tangential discharge passage 43b opening to atmosphere through the side of the generator.

In operation, the generator of FIGS. 36 behaves similarly to that of FIGS. 1 and 2. The balls 44 exert their centrifugal forces directly against the body 41b while rolling on the peripheries 42a of the circular chambers 42. As described in connection with the preceding embodiment, random force impulses exerted against the lower end of the rod 41 tend to set the latter into a halfwave mode of resonant longitudinal elastic vibration, the balls coming up to resonant speed one after the other, each further amplifying the resonant vibration of the rod 41, and thus strengthening the resonant back reaction or feedback by which the balls are controlled to spin at resonant frequency under dominance by the resonance in the bar. This manifestation of resonance thus again tends to synchronize the balls 44 to move vertically in perfect unison with one another. The process gradually but quickly builds up toward maximum standing wave amplitude for the rod 41. As in the preceding embodiment, the balls are not only synchronized in the first instance with the resonant frequency vibration in the bar by operation of a phenomenon arising out of resonance, they are thus thereby also synchronized with one another. To summarize in other language, the balls are locked in at the resonant periodicity of the bar 41, just below peak resonance amplitude, by a back reaction or feedback effect which rises rapidly and disproportionately (more than proportionately) with and by virtue of the approach to peak resonance. The balls are thus controlled against overspeeding or going out of synchronism with one another or with reference to the longitudinally vibrated bar 41.

The upper end of the bar 41 will be understood to vibrate the bottom wall of the tank 41a. The purpose may be sonic treatment of the liquid contained within the tank, or sonic treatment of articles suspended within the liquid in the tank, as in the case of sonic polishing of articles by liquid carrying finely divided abrasive particles. Again, the particular application does not form part of the invention claimed herein, and need not be further described.

With reference to elastic elements 10, 41 and 41a, it will be noted that their dimensions are sufficiently large so as to have a reasonable resonant frequency relative to the dimensions of the rotor bearing means, such as 31 or 42a.

It is important to note that this tendency for desirable interphasing of the several rotors, which is accomplished by this invention as above explained, is of benefit no matter how the several rotors are driven. Accordingly, it is important to recognize that this invention is not limited to fluid driven rotors, but is also effective with other variations of my invention including systems where the several rotors are direct driven mechanically by motor means or by magnetic field forces, such drives being shown, for example, in the aforementioned Patent No. 2,960,314.

What is claimed is:

1. In a sonic vibration process, the steps of: driving a plurality of inertia rotors repeatedly in orbital paths around the surface of a corresponding plurality of cylindrical bearings, holding said bearings in coupled relation to a vibratory part of an elastically vibratory apparatus, and driving said inertia rotors with sufficient effort to cause them to revolve in said orbital paths in the resonant frequency range of said elastically vibratory apparatus but with insuificient effort to obtain peak resonant amplitude of said vibratory part thereof, so that said inertia rotors all assume and hold a synchronous relation to the vibration of said vibratory part below the frequency for said peak amplitude.

2. The method of claim 1 wherein at least one pair of said inertia rotors is caused to revolve in said resonant range and the individual rotors of said pair revolve in opposite directions of rotation.

3. The method of claim 1 wherein said inertia rotors are caused to revolve in said resonant range and the inertia masses of said rotors revolve in orbital paths inside of said bearings.

4. The method of claim 1 wherein said rotors are caused to revolve in said resonant range and the inertia masses of said rotors revolve in orbital paths outside of said bearings.

References Cited by the Examiner UNITED STATES PATENTS 2,420,793 5/ 1947 OConnor 2591 2,496,291 2/ 1950 High. 2,675,777 4/ 1954 Lachaise.

FOREIGN PATENTS 3 87,473 2/ 1933 Great Britain.

WALTER A. SCHEEL, Primary Examiner.

I. BELL, Examiner, 

1. IN A SONIC VIBRATION PROCESS, THE STEPS OF: DRIVING A PLURALITY OF INERTIA ROTORS REPEATEDLY IN ORBITAL PATHS AROUND THE SURFACE OF A CORRESPONDING PLURALITY OF CYLINDRICAL BEARINGS, HOLDING SAID BEARINGS IN COUPLED RELATION TO A VIBRATORY PART OF AN ELASTICALLY VIBRATORY APPARATUS, AND DRIVING SAID INERTIA ROTORS WITH SUFFICIENT EFFORT TO CAUSE THEM TO REVOLVE IN SAID ORBITAL PATHS IN THE RESONANT FREQUENCY RANGE OF SAID ELASTICALLY VIBRATORY APPARATUS BUT WITH INSUFFICIENT EFFORT TO OBTAIN PEAK RESONANT AMPLITUDE OF SAID VIBRATORY PART THEREOF, SO THAT SAID INERTIA ROTORS ALL ASSUME AND HOLD A SYNCHRONOUS RELATION TO THE VIBRATION OF SAID VIBRATORY PART BELOW THE FREQUENCY FOR SAID PEAK AMPLITUDE. 